The present invention relates to disk circuits and, more particularly, to a method and apparatus for reading information from a magnetic disk by biasing a read head.
Conventional magnetic storage devices include a magnetic transducer or xe2x80x9cheadxe2x80x9d suspended in close proximity to a recording medium, for example a magnetic disk having a plurality of concentric tracks. The transducer is supported by an air-bearing slider mounted to a flexible suspension. The suspension, in turn, is attached to a positioning actuator. During normal operation, relative motion is provided between the head and the recording medium as the actuator dynamically positions the head over the desired track. The relative movement provides an airflow along the surface of the slider facing the medium, creating a lifting force. The lifting force is counterbalanced by a predetermined suspension load so that the slider is supported on a cushion of air. Airflow enters the xe2x80x9cleadingxe2x80x9d end of the slider and exits from the trailing end. The air is used to prevent the head from contacting the disk, which would result in damage.
Writing data is typically performed by applying a current to the coil of the head so that a magnetic field is induced in the adjacent magnetic-permeable core, with the core transmitting a magnetic signal across any spacing and protecting the coating of the disk to magnetize a small portion of the digital bit of the medium within the disk.
Reading of the information in the disk is performed by sensing the change in magnetic field of the core as the transducer passes over the bits in the disk. The changing magnetic field induces a voltage or current in the inductive leak coupled coil. Alternatively, reading of the information may be accomplished by employing a magneto-resistive (MR) sensor, which has a resistance that varies as a function of the magnetic field adjacent to the sensor. In order to increase the amplitude and resolution in bits, the MR sensor is typically positioned on a slider as close to the disk as possible. Connected to these heads are sensors and read circuits which amplify the recorded data and eliminate noise.
Most differential pre-amps in use today require a constant voltage across the read head. This constant voltage is achieved by using a negative feedback loop. However, these pre-amps typically have several dominant poles, and these dominant poles are close to each other in frequency. These dominant poles can cause instability in the feedback loop, and the instability can lead to a significant overvoltage, which can destroy the MR head. Additionally, the instability can cause significant ringing of the head voltage, which will not allow the head to operate at its optimum bias voltage. Thus, there is a need for a circuit, which will eliminate these problems.
The present invention includes a constant voltage circuit, which reads information from a head and does not cause instability in the feedback loop. The present invention provides for a constant voltage circuit that moves the dominant poles apart in frequency allowing the feedback loop to operate without oscillation.